There are clearly substantial similarities between these lists, indicating that this could be an effective replacement. However, without a test, it's nearly impossible to tell.

There are certainly reasons to root for Monistat's efficacy. The big one, of course, is value.

Monistat costs $5.99 for 1.5oz, or $3.99 per ounce. Smashbox, however, is $36 for 1 ounce. That means that Smashbox is over nine times more expensive than Monistat.

The appearance and initial feel of the product is virtually identical.

Monistat on the left, Smashbox on the right.

For this test, I decided that using a single foundation was a bit unfair, since sometimes primers handle different foundations differently. I decided to use three foundations. They were chosen based on what I had on hand. The three were:
Maybelline Dream Liquid Mousse,
Lancome Tient Idole Ultra 24 Hours, and
Tarte Amazonian Clay 12 Hour Full-Coverage Foundation.

In order to test for opacity (which is awfully important for those of us who want to cover up our acne), I layered the primer and foundation over a stripe of red and a stripe of black.

I also decided to use a control over no primer at all. This would ensure that we could gauge if the primer is doing its job.

'C' refers to control, 'M' to Monistat, and 'S' to Smashbox

There was no initial effect of primer on opacity.

Four hours later...

Four hours after the foundation application, though, there were definitely noticeable differences. The picture is a little bit difficult to interpret, though, so let's be clear about what you are seeing: For the Maybelline foundation, both the control and the Monistat conditions were almost completely faded away. The Smashbox primer maintained a bit of opacity, however, performing better than both the control and the Monistat condition. For the Lancome foundation, Monistat performed worse than the control. Smashbox, on the other hand, performed better. For the Tarte foundation, Monistat, again, performed worse than the control. Smashbox seemed to perform about the same as the control.

In summary, Smashbox performed better than the control in two out of three conditions, and performed the same as the control in one. Monistat performed the same as the control in one condition and worse than the control in two out of three. Smashbox outperformed Monistat in every single condition.

That is not the mark of an effective dupe. Indeed, given that Monistat did WORSE than the control, it looks like it is causing makeup to rub off, not anchoring it in place. Despite the similar ingredients, the proportion of ingredients is different. Since Monistat is not formulated as a primer, it should hardly be shocking that the ratio is not ideal for makeup application.

To double check that my findings applied to my actual face, I did another experiment. Half my face was applied with Monistat and half with Smashbox. I found that, the Monistat side had more problems. What's more, the places where I had blemishes were most susceptible to makeup rubbing off. For me, that's by far the most important place for my foundation to stay put. The Smashbox side did not have these problems.

It is worth noting that there are additional benefits of a primer that were not measured in this test. However, in terms of makeup wear-time, my test suggests you would be better off not wearing a primer at all than wearing Monistat. You're not saving money if your primer is actually making things worse.

I've heard so many good things about their primers. I've never used anything actually by smashbox, but I know it is supposed to be top notch. I might have to treat myself this weekend :) xHeroine In Heels